Conveying system for particulate materials



Oct. 5, 1965 w. M. BOOTH ETAL CONVEYING SYSTEM FOR PARTICULATE MATERIALS2 Sheets-Sheet 1 Filed Jan. 31, 1963 INVENTORQ W/ZHAM M. BOOTH BET/V44 06'. k/lff ATTORNEY United States Patent 3,210,131 CONVEYING SYSTEM FORPARTICULATE MATERIALS William M.'Booth, Grand Haven, and Bernard G.Witte, Newaygo, MiCh., assignors to Newaygo Engineering Company,Newaygo, Mich., a corporation of Michigan Filed Jan. 31, 1963, Ser. No.255,242 3 Claims. (Cl. 302-53) This invention relates to a pneumaticconveying system for particulate materials, and more particularly forfoundry sand.

This application is a continuation-in-part of application Serial No.58,550 filed September 26, 1960, now abandoned, of William M. Boothentitled Conveying System for Particulate Materials.

Usually, foundry sand is conveyed from one point to another in a foundryby conveyor belts. However, conveyor belts are slow and are unable tohandle the large amounts of sand necessary to supply the needs of amodern high-capacity foundry. It has therefore been proposed in the pastto convey sand pneumaticall from one foundry station to another. Priorinstallations of this type have used pressure-tight transporter hopperswhich were charged with sand. Compressed air under high pressure wasthen introduced into the top of the hopper to push the sand downwardinto a conveying tube. This system had several drawbacks; first, foundrysand, particularly after it has gone through the muller, is veryadherescent and therefore tended to compact in the transporter hopperand clog the conveyor tube.

For the same reason, it was necessary to provide large conveyor tubeswith very gradual bends in them. The necessity for gradual bends in thetube often required considerable excavation in prior art installationsbecause the transporter hopper could not be mounted high enough abovethe floor of the foundry to lead the conveyor tube away from it at therequired radius without going below the floor level. When the system didoperate, the friction of the sand against the outside walls of the tubein the gradual bends would cause such substantial abrasion of theconveyor tube that expensive repairs had to be undertaken at frequentintervals. Furthermore, a considerable amount of compressed air wasrequired to transport the sand in these prior art applications; atypical such installation would, for example, transport three to fourpounds of sand per cubic foot (at atmospheric pressure) of compressedair. Finally, the rapid transport of the sand in these priorinstallations, as compared to conveyor belt installations, did notpermit the used sand to cool to handling temperatures before beingdelivered back to the molding station, so that expensive cooling deviceswere required.

It was next proposed in US. Patent No. 2,794,686 (now Re. 24,716) toimprove the flow of sand through the conveying pipe by providing thebase of the transporter hopper with a ring of air jets to continuouslystir the sand in the hopper during transportation and by providingboosters at intervals along the conveying pipe in which similar rings ofjets theoretically imparted a helical motion to the sand to preventclogging during the conveying process. This system, however, reducedfriction of the sand against the pipe Walls only partially, and thediscreteness of the air jets caused heavy turbulence and severe abrasionof the equipment in the vicinity of the jets. Also, the abrasion causedby centrifugal forces in bends of the pipe still caused heavilyunilateral wear of the pipe on the relatively weak outside wall of thebend.

The present invention overcomes all these problems by providing for theintroduction of the compressed air into both the hopper and the pipe ina continuous, uniform, spirally rotating laminar flow in such a mannerthat the sand is in effect held in suspension throughout the system awayfrom the Walls of the system and is simul taneously maintained insufficient agitation to prevent its compacting. This improvement resultsnot only in considerably less wear by greatly reducing sand frictionagainst the hopper and conduit walls, but it also permits a much moreefficient utilization of the compressed air. For example, a typicalinstallation according to this invention can transport six to eightpounds of sand per cubic foot of air. The suspension action whichreduces abrasion and prevents compacting of the sand furthermore makesit possible to use much smaller conveying pipes with sharp bends. Thisin turn has two advantages: first, excavations are no longer necessarybecause the conveying pipe can be laid entirely above ground; second,experience has shown that pads of compacted foundry sand from along theoutside walls of the conveying pipe in the sharp bends. These sand padsabsorb the impact of the conveyed sand particles and greatly reduce theabrasion of the pipe at the bend.

The sudden expansion of the compressed air as it leaves the annular jetscauses this air to become highly chilled. Due to the much greaterquantity of air delivered by the annular jet of this invention ascompared to the discrete jets of the prior art, the air in the presentsystem cools the sand to a considerable degree, thus dispensing with thenecessity for special cooling apparatus.

It is therefore the primary object of this invention to provide a fast,efficient, wear-resistant pneumatic conveying system for foundry sandhaving a high sand-to-air ratio.

It is a further object of this invention to provide a pneumaticconveying system for particulate materials which requires no specialexcavations or other construction measures.

It is another object of this invention to provide a foundry sandhandling system in which the sand is substantially suspended by arotating, laminar air cushion in spaced relation to the walls of theconveying components during the conveying process.

It is yet another object of the invention to provide for rotation of thesand-supporting laminar conveying air film in a direction compatiblewith the forces arising from the earths rotation.

It is yet a further object of the invention to provide for discharge ofthe conveying air at an angle to adjacent walls of the conveyingcomponents so as to combine maximum conveying efiiciency with minimumwear.

It is a still further object to provide a pneumatic foundry sandhandling system which is free from bridging even when highly adherescentsand is used.

It is still another object of this invention to provide a foundry sandhandling system which makes it possible to cool the sand while it isbeing conveyed.

These and other objects of this invention will become apparent from aperusal of the following specification, taken in connection With theaccompanying drawings in which:

FIG. 1 is a diagrammatic elevation of a system constructed according tothis invention;

FIG. 2 is a fragmentary vertical section through one form of transporterhopper which can be used in the system of FIG. 1;

FIG. 3 is a horizontal section along line IIIIII of FIG. 2;

FIG. 4 is a detail vertical section of the impeller manifold along lineIV1V of FIG. 3;

FIG. 5 is a vertical section through the conduit jet; and

FIG. 6 is a vertical section along line VI-VI of FIG. 5.

Basically, the system of this invention uses a pressuretight hopper(generally referred to hereinafter as the transporter hopper) into whichcharges of particulate material,

such as foundry sand, are intermittently introduced. (The resultingintermittent operation of the system can be eliminated by providing twotransporter hoppers connected to the same conveying conduit by switchmeans such as that disclosed in the copending application Serial No.236,930 filed November 13, 1962 and entitled Switch for PneumaticConveyors. In such an installation, one transporter hopper can becharged while the other is conveying.) Pressure means such as compressedair are provided to create a pressure in the transporter hopper so as tobias the particulate material toward the conveying conduit. Thecompressed air is introduced into the transporter hopper in a generallytangential direction so as to provide a continuous, swirling laminar airflow along the walls of the transporter hopper which in effect suspendsthe sand in spaced relation to the walls of the hopper during theconveying process. This effectively reduces adhesion of the material tothe sides of the hopper, bridging of the material across the conveyingconduit, and abrasion of the hopper walls. In accordance with one aspectof the invention, abrasion is further reduced by discharging the airstream into the hopper at an acute angle to the hopper walls, ratherthan parallel thereto.

Jet means are provided in the conveying conduit near the transporterhopper to draw the particulate material out of the transporter hopper,thus assisting the action of the pressure means in the transporterhopper itself. Compressed air is introduced tangentially into theconduit jet means so that it exits from the jet in a continuous,spiraling laminar stream forming a revolving cylindrical air cushionwhich keeps the particulate material away from the inner walls of theconveying conduit. The particulate material is thus substantiallysuspended in the center of the conveying conduit. Unlike theindividually oriented, discrete jets of the prior art, the laminar jetof this invention creates a distinct vacuum (about ten pounds per squareinch) in the transporter hopper when the conduit jet is operated alone.This vacuum effect considerably increases the transporting power of theimpeller. The sudden expansion of the compressed air as it leaves thejets also chills the air so that the particulate material is cooledthereby during the conveying process.

For the same reason as mentioned above in connectionwith the hopper, andalso because of the desirability of avoiding discontinuities in theconveying conduit, the air stream of the conduit jet is introduced intothe conduit at an angle to the conduit walls.

In both the impeller and the conduit jet, another aspect of theinvention teaches that counterclockwise rotation of the laminar aircushion, in the direction of conveying, materially improves theperformance characteristics of the system. This improvement is due tothe action of the earths rotational forces in the Northern Hemisphere onthe revolving air cushion.

It the system is used to convey foundry sand, sharp bends may bepurposely formed in the conveying conduit to cause the formation of padsof compacted foundry sand along the walls of the conveying conduit onthe outside of the bend. These sand pads absorb the impact of the sandparticles as they go around the bend and thus reduce abrasion of theconveying conduit at the bend.

At the end of the conveying conduit, the particulate material istangentially introduced into a cylindrical receiving hood which slowsthe particles down by friction against the walls of the hood. The slowedparticles then are allowed to drop by gravity into a receiving containersuch as a bin.

' Referring now to FIG. 1, foundry sand 20 coming, for example, from amuller (not shown), arrives by any suitable transportation means such asconveyor belt 22 and is dumped into the storage bin 24. A transporterhopper 26 is located underneath the storage bin 24 and is adapted toreceive sand therefrom when the cover 28 of transporter hopper 26 isopened. Suitable means for accomplishing this are shown in the copendingapplication Serial No. 175,993 filed February 27, 1962, and entitledValve for Pressurized Hopper.

A compressor 31) cooperating with an air tank 32 and a pressureregulator 34 supplies compressed air at a constant pressure of e.g. onehundred pounds per square inch to the air system 36 which suppliescompressed air to the impeller 46) and jet 42 through control valves 44,45, respectively. If desired, the top of hopper 26 may also bepressurized. An atomizer 46 may be provided in the jet air line 48 tointroduce a finely dispersed treating agent into the conveying conduitor pipe 50 is desired.

Sand pads 52 which form in the portions 54, 56, and 58 of the conveyingpipe 50 provide abrasion resistance to the (normally thin) outerportions of the bends of the conveying pipe 51).

One end 60 of the conveying pipe 50 is connected to the impeller 41? atthe bottom of the transporter hopper 26, while the other end 62 of theconveying pipe 50 is tangentially connected to a cylindrical receivinghood 64 in which the arriving sand is slowed by rubbing against the sidewalls 66 of hood 64 under the influence of centrifugal force. The slowedparticles 68 then fall under the effect of gravity into the receivingbin 70 which may be positioned, for example, at a molding station 72.

FIG. 2 shows the frustoconical bottom or funnel portion 76 of thetransporter hopper 26. The impeller 40 is mounted between the bottomhopper flange 106 and the conveying pipe entrance flange 110 by bolts108. Seals 112 and 113 keep the impeller pressure-tight. In order tocreate the previously mentioned swirling or suspension action,compressed air is introduced into the impeller manifold chamber 114 bytangential air intakes 116 (FIG. 3). Air escapes from the impellermanifold chamber 114 into hopper 26 through the annular nozzle 118. Theeffective air discharge area of nozzle 118, and hence its air flowcharacteristics, can be adjusted by an appropriately size nozzle ring120. To prevent sand from falling into the impeller manifold chamber114, a resilient seal 122 is provided adjacent the nozzle ring 118 toact as a check valve which permits compressed air to travel upward butprevents sand from traveling downward. The resilient seal 122 and thenozzle ring are fastened to the impeller 41 by a retaining ring 124 andscrews 126. The impeller 40 has a central opening 128 through which thesand in the transporter hopper 26 can pass into the conveying pipe 50.

As will be best seen in FIG. 4, the walls of the nozzle 129 are inclinedabout fifteen degrees with respect to the inner, preferablypolyurethane-lined wall 84 of the frustoconical hopper section 76. Thisinclination takes into account the fact that the air emerging from thenozzle 129 is decompressed as it enters the hopper 26 and thereforeforms a divergent pattern whose angle of divergence d has beenempirically determined to be about fifteen degrees on each side of thesurface of the imaginary cone 0 defined by the parallel walls 80, 82 ofthe nozzle 129. The inclination of the nozzle 129 with respect to thewalls 84 not only produces a more uniform laminar air flow along thewall 84, but also eliminates the serious abrasion effects by whichunavoidable impurities in the compressed air previously scored theanti-adherescent polyurethane lining 78 and even the steel wall 84 sobadly that the useful life of the hopper 26 was greatly shortened.

A preferred form of conduit jet according to this invention is bestshown in FIGS. 5 and 6. In FIG. 5, 130 is the downstream end of theportion of conveying pipe 50 which was designated by the numeral 54inFIG. 1. The jet 42 is inserted between the pipe end 130 and the upstreamend 132 of the pipe section leading to element 56 in FIG. 1 and fastenedthereto by appropriate means such as 134. The jet 42 includes a pair ofend pieces 135, 137 held together by bolts 139. The end pieces 135, 137clamp between them a manifold assembly composed of three rings 141, 143,which are secured together by b ll 147 and define an annular manifoldchamber 136.

Compressed air is tangentially introduced into the manifold chamber 136by tangential air intakes 138. The walls 148, 150 of the rings 141, 145define between them a frustoconical nozzle 140 which opens into theconduit 50. It will be noted from FIG. 5 that the jet 42 is soconstructed that there is no discontinuity in conduit 50 throughout thejet 42 except for the actual discharge opening of the nozzle 140 itself.This construction significantly reduces the turbulence at jet 42 andaids in the rapid creation of a smooth air cushion downstream of jet 42.Air is discharged in a spiraling laminar pattern from the annular nozzle140 and expands in the conveying pipe 50 into a divergent patternsimilar to that discussed herein-' above in connection with the impeller40. The rapid forward motion and large quantity of the air dischargedfrom nozzle 140 creates a vacuum upstream of jet 42 which draws sand outof the portion 54 of pipe 50 and hence out of the transporter hopper 26.

In order to compensate for the convergence of the air stream at the exitfrom the nozzle 140, the surface of the imaginary cone 0' defined by thenozzle 140 is disposed at a fifteen degree angle to the conduit wall152. The rapid spinning motion of the air stream as it travelsdownstream in the conduit 50 quickly causes the convergence forces to beovercome by the centrifugal forces acting on the air molecules, so thatthe air stream quickly settles into a cylindrical air cushion spiralingforward along the wall of the conduit 50.

In accordance with one aspect of the invention, the air is so introduced(FIG. 6) into the manifold 136 by intakes 138 as to causecounterclockwise (looking downstream) spinning of the air emerging fromnozzle 140. This is the natural spin direction in the northernHemisphere, and it has been found that if this spin direction is notobserved, a reversal of the spin direction occurs in the pipe 50 at somedistance from the jet 42, and clogging of the pipe is apt to result atthat point, particularly if the conveyed sand is very humid. By using acounterclockwise spin, no such reversal occurs, and the necessity forboosters at intervals along the pipe is eliminated for all practicalpurposes.

For a like reason, the impeller 40 is arranged, as best shown in FIG. 3,to produce a counterclockwise (look ing downward in FIG. 3) rotation ofair. It has been found that this feature greatly reduces short-circuits,i.e. air flow directly from the impeller into the pipe while a bridge ofcompacted sand remains intact above the air current in the hopper.

Assembly The system is assembled as shown in FIG. 1. The valves 44, 45may, if desired, be connected to an appropriate control system adaptedto operate them in the proper sequence for automatic operation ashereinafter described. If two transporter hoppers are used, a switchsuch as that shown in FIG. 6 of the aforesaid copending applicationSerial No. 236,930 may be provided in the conveying pipe 50 either aheadof or beyond the jet means 42.

Operation When it is desired to convey sand from the storage bin 24 tothe receiving bin 70, the cover 28 is opened and a charge of sand isintroduced into the transporter hopper 26 from storage bin 24. When thetransporter hopper 26 is almost completely filled, the cover 28 isclosed and the valve 44 is operated to supply compressed air to theimpeller 40. This causes the sand to become suspended within thetransporter hopper 26 and the pipe 50. When the air pressure within thehopper 26 reaches approximately twenty pounds per square inch, the sandbegins to move into the pipe 50. At that pressure, valve 45 is operatedto power the jet 42, and the material is thereupon conveyed aconsiderable speed out of the transporter hopper 26 and through the pipe50 due to the dual action of the pressure created by impeller 40 and thevacuum created by jet 42. The delaying of the actuation of jet 42 untilconveying pressure has been built up in the transporter hopper 26reduces the possibility of short-circuiting the air flow in the hopper26 by withholding the vacuum effect from jet 42 until the suspension ofthe material in hopper 26 has become complete.

If desired, the atomizer 46 may be filled with an appropriate treatingliquid, and the sand passing by jet 42 will then be treated with thisliquid in fine dispersion. In any event, the cooling of the air as itexpands upon entering pipe 50 causes a considerable cooling of the sandas it travels through pipe 50. The sand is eventually discharged at theother end 62 of conveying pipe 50 into the cylindrical receiving hood64. There, it is thrown against the walls 66 of hood 64 by centrifugalforce and is thus slowed down until gravity causes it to drop into thereceiving bin 70.

It will be seen that this invention provides a highcapacity pneumaticconveying system which can be installed in low space, i inexpensive toinstall, operate, and maintain, and which permits a highly efiicientutilization of the pneumatic medium and permits the cooling and treatingof the conveyed material in transit. Obviously, the invention can becarried out in numerous ways of which the illustrative embodiment shownis merely one example. Consequently, the invention is not intended to belimited by the embodiment shown herein, but solely by the scope of thefollowing claims.

We claim:

1. A pneumatic hopper assembly for particulate materials comprising: apressure-tight hopper; controllable inlet means into the top portion ofsaid hopper for material to be conveyed; said hopper having a generallyfrustoconical, downwardly convergent bottom wall and an outlet at thebase thereof; conveying conduit means connected to said outlet; anannular pressure manifold around said frusto-conical bottom walladjacent the base thereof; pressurized fluid inlet means into saidannular chamber, tangentially thereto; a continuous annular outlet slitin said bottom wall, communicating with said manifold, and directedupwardly into said hopper along said frustoconical wall, causing thepressurized gases introduced tangentially into said annular manifold toswirl out of said slit in a continuous spiraling laminar film along saidhopper wall to suspend the particulate materials thereagainst; and meansto form a pressure differential between said conveying conduit means andthe top of said hopper to force the suspended materials through saidoutlet.

2. The assembly in claim 1 in which said tangential fluid inlet means tosaid manifold is arranged to create counterclockwise spiraling towardsaid conduit means from said hopper.

3. The assembly in claim 1 including an annular nozzle around saidoutlet and adjacent said frusto-conical wall to form said annular slit,and having between them an angle generally equal to half the divergenceangle of the pneumatic fluid stream discharged from said slit.

References Cited by the Examiner UNITED STATES PATENTS 2,027,697 1/36Nielsen 302-5 3 2,794,68 6 6/5 7 Anselman 303-5 3 FOREIGN PATENTS707,791 7/ 41 Germany. 325,544 2/30 Great Britain.

SAMUEL F. COLEMAN, Primary Examiner.

ANDRES H. NIELSEN, ERNEST A. FALLER,

Examiners.

1. A PNEUMATIC HOPPER ASSEMBLY FOR PARTICULATE MATERIALS COMPRISING: APRESSURE-TIGHT HOPPER; CONTROLLABLE INLET MEANS INTO THE TOP PORTION OFSAID HOPPER FOR MATERIAL TO BE CONVEYED; SAID HOPPER HAVING A GENERALLYFRUSTOCONICAL, DOWNWARDLY CONVERGENT BOTTOM WALL AND AN OUTLET AT THEBASE THEREOF; CONVEYING CONDUIT MEANS CONNECTED TO SAID OUTLET; ANANNULAR PRESSURE MANIFOLD AROUND SAID FRUSTO-CONICAL BOTTOM WALLADJACENT THE BASE THEREOF; PRESSURIZED FLUID INLET MEANS INTO SAIDANNULAR CHAMBER, TANGENTIALLY THERETO, COMMUNICATING ANNULAR OUTLET SLITIN SAID BOTTOM WALL, COMMUNICATING WITH SAID MANIFOLD, AND DIRECTEDUPWARDLY INTO SAID HOPPER ALONG SAID FRUSTOCONICAL WALL, CAUSING THEPRESSURIZED GASES INTRODUCED TANGENTIALLY INTO SAID ANNULAR MANIFOLD TOSWIRL OUT OF SAID SLIT IN A CONTINUOUS SPIRALING LAMINAR FILM ALONG SAIDHOPPER WALL TO SUSPEND THE PARTICULATE MATERIALS THEREAGAINST; AND MEANSTO FORM A PRESSURE DIFFERENTIAL BETWEEN SAID CONVEYING CONDUIT MEANS ANDTHE TOP OF SAID HOPPER TO FORCE THE SUSPENDED MATERIALS THROUGH SAIDOUTLET.